Method performance terms true value

The split-amplitude strategy represents the total amplitudes as the sum of an a priori known approximate value, obtained from some external source, and an unknown correcting term. Assuming, further, that the known amplitudes represent a good approximation to the true ones, the unknown corrections can be obtained to a high degree of accuracy from a set of linear equations. The results of this article show that when a proper reference space is used, the connected clusters obtained from the MR CISD wave function represent indeed a very good approximation, and the almost linear versions of the RMR CCSD method performs very well. 

A method performance characteristic generally expressed in terms of the signal or measnrement (true) value... 

The performance of measurement systems has been traditionally defined in terms of accuracy and precision. Accuracy can be defined as a measure of how close a result is to the actual value and precision is thought of as the uncertainty of the result, which we could identify with the standard uncertainty. Modem usage in the context of quality of analytical results tends to avoid these terms. This is because there has been a more fundamental appreciation of the actual measurement process. For example, accuracy or, perhaps we should say, inaccuracy, involves bias within a measurement process as well as statistically determined factors that cause the result to be different from the true result What, at one time, we would have blithely termed precision is now discussed as repeatability, the variability of a method when applied to measurements on a single sample within a laboratory, and reproducibility, which applies to measurements of that sample when appUed by different laboratories using different instruments operated by different operators. 

However, each method will certainly give rise to more or less random errors which govern what we prefer to term its precision. If these random errors obey a Gaussian distribution they are characterized by a standard deviation, sufficiently large number of replicate determinations. The range on each side of any one experimental result in which the true result may lie will depend upon the v value for the determination concerned and the degree of probability with which we are satisfied. In most industrial measurements the 95% confidence limit, which is approximately 2a, is considered adequate and 2[Pg.5]

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